Bitpit

- modified main script to accept multiple urls and accept -r and -m options.

- changed ``min_period`` property name in Manager class to ``restart_wait``
to match the naming of Downloader class.
- changed the meaning of ``restart_wait`` property in Manager class to mean
the minimum time to keep a download paused before it is started again. now
manager updates can happen frequently if needed but a single download will
not be started too frequently.
- changed in internal implementation of restart thread in Downloader and in
schedule thread in Manager. now both use Timer class from threading
module.
- minor changes in tutorial.

- Emitter class:
- emit() no longer gives self as an argument.
- emit() takes *args positional arguments that will be passed to
callbacks.
- listen() now takes *args and **kwargs. these will be passed to
callbacks. *args in emit() come first before *args in listen().
- unlisten() now takes *args and **kwargs. these must be the same values
passed to listen() in order to unlisten the callback.
- Downloader class:
- rearranged constructor arguments order to make more frequently used
arguments first.
- changed ``chunk_size`` default value to 4 KB.
- added ``dir_path`` argument.
- rewritten attributes using property decorator with some attributes
writable while others are only readable.
- added ``restart_time`` property.
- changed ``start`` state to mean the downloader just started but no
downloading is actually happening. only attempting to connect.
- added ``download`` state.
- now ``error`` state means an error occured and it is expected to be
temporary.
- added ``fatal-error`` state for errors that are expected to reoccure
if the download is restarted. no automatic restart happens if the
downloader stopped due to fatal error.
- added the following signals:
- url-changed
- path-changed
- restart-time-changed
- rate-limit-changed
- when the downloader gets the file size, it only emits ``size-changed``
signal when the new size is different from the old size.
- modify all emit() calls to keep the behaviour of previous version
after changing Emitter methods listen(), unlisten() and emit().
- added Manager class
- update documentation and add library reference.

- initial release